Thermal (heat-sensitive) recording materials express image areas and non-image areas as temperature difference distribution and a number of system have been contrived, including fusion transfer and sublimation transfer of colorants, color development reaction between two components induced by heat fusion or breakage of capsules, and changes in optical characteristics by phase transition. The thermal recording media of this kind have been widely used as output materials for various printers, word processors and facsimile devices, because they have the advantages of producing recorded images by dry and simple systems and being maintenance-free as well. With the recent progress in laser recording equipment, their applications to optical disks and platemaking materials have also been investigated.
Although silver halide photosensitive materials requiring wet processing have been conventionally used as the platemaking materials, the development of dry processes has been desired from a request for simplification of processing steps and the problem of environmental pollution caused by processing solutions, and some technical proposals referring to thermal recording systems have recently been made. From the viewpoint of resolution, image recording with lasers is preferred, and for example, a system called dye ablation, in which a high output laser is used, has been developed. Recording materials used in the system are disclosed in JP-A-7-164755 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-7-149063, JP-A-7-149065, and image formation devices in JP-A-8-48053, JP-A-8-72400. In this system, a recording material having a dye composition applied onto a support, said dye composition comprising an image dye, a substance having absorption in a laser wavelength region (infrared absorber) and a binder, is irradiated with a laser beam from the dye layer side thereof to achieve image recording. Energy given by a laser causes abrupt local changes at spots on the image forming layer which the laser beam strikes, thereby expelling substances from the layer. The above-mentioned patent specifications say that the changes are not completely physical ones (for example, fusion, evaporation or sublimation), but some kinds of chemical changes (for example, bond breakage), and that they are not partial removal of the image dye, but complete removal thereof. Such a dye ablation system has the disadvantages that a high output laser is indispensable to increase the efficiency of dye removal at sites exposed to the laser beam, and that a collector for collecting removed dye must also be installed.
As a system requiring no collector, U.S. Pat. No. 5,171,650 discloses an image recording method of an ablation transfer system in which a laser is used as a heat source. In this system, a dye donor sheet is used which comprises a dynamic separation layer coated with an ablative carrier topcoat, and an image is transferred to another receiving sheet which is aligned adjacent to the dye donor sheet. Accordingly, this system has the disadvantage of leaving a disused sheet as a waste material after image recording. In addition, also in this case, a high output laser is indispensable in order to increase transfer efficiency. Thus, customary thermal recording systems utilizing ablation with lasers have the disadvantages that the high output laser is needed, and that dust or waste materials are unavoidably generated.
Further, a thermal recording system developed from the system called "dry silver", without ablation utilizing a laser, is described in JP-A-6-194781. In this system, recording is conducted with a laser to a recording material comprising a thermally reducible silver source, a reducing agent for a silver ion and a light-heat conversion dye. However, the keeping quality of non-image areas and the heat sensitivity are practically insufficient.
Also, as other heat sensitive recording method which uses laser, compounds whose absorption changes by thermal decomposition of carbamate are described in U.S. Pat. No. 4,602,263 and U.S. Pat. No. 4,826,976. In addition, a compound which develops yellow color by thermal decomposition of an alkoxycarbonyl group introduced into hydroxyl group is described in U.S. Pat. No. 5,243,052, and compounds which develop yellow, magenta and cyan colors by thermal decomposition of an alkoxycarbonyl group introduced into hydroxyl group are described in JP-A-4-124175, JP-A-5-2748342, JP-A-6-227139, JP-A-5-281654 and JP-A-6-255256 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). Though these methods use an irreversible monomolecular reaction and are suited for laser-aided image recording for an extremely short period of time, their sensitivity is not sufficient so that more higher sensitivity is desired. In this connection, the alkoxycarbonyl group of the present invention is not described in these patents.
In addition, as a method for forming an ultraviolet mask image (360 nm to 420 nm; corresponding to an exposure light source to a presensitized plate) used for a platemaking material, no practical proposal has been made for the heat mode system utilizing a laser.
On the other hand, there are known benzotriazole compound-containing thermal recording materials described in JP-A-9-95487. However, the benzotriazole compounds described in this patent specification differ from those of the present invention, and are used as ultraviolet absorbers for improving the keeping quality of thermal recording images, but not for forming images to ultraviolet light.